Massive, gauge-singlet vector bosons are common ingredients of many theories beyond the SM, typically appearing as gauge bosons of larger symmetry groups that are broken to the SM one. As such they appear frequently in models with a gauged \(B-L\)  charge, models of compositeness or theories with extra dimensions (see [1]} for a comprehensive review). In the context of the persisting \(B\) -physics anomalies, they have raised interest as potential mediators of the \(b\rightarrow s{\hspace{0.85358pt}}\ell ^+\ell ^-\)  anomalies [2]}, [3]}, [4]}, and they are part of the new-physics spectrum of more comprehensive models offering combined explanations of the anomalies in \(b\rightarrow s\ell ^+\ell ^-\)  and \(b\rightarrow c\ell ^-\bar{\nu }\)  transitions [5]}, [6]}. Even though the main mediators in the latter models are vector leptoquarks, it can be shown that a \(Z^{\prime }\)  boson cannot be avoided in such constructions [7]}. The framework outlined in this paper can be used to describe the decays of heavy vector resonances into SM fields, including the sizable resummation effects affecting the decay rates, in an economic and systematic way.
